There are a number of surgical techniques for treating clouding of the lens, referred to as a cataract or being pearl-eyed. The most common technique is phacoemulsification, in which a thin tube in the form of a hollow needle is inserted into the ocular lens and excited to oscillate via ultrasound. The vibrating needle emulsifies the lens in the direct vicinity thereof such that the lens fragments generated can be suctioned away through a line via a pump. Once the lens has been completely emulsified, a new artificial lens can be inserted into the empty lens capsule and so a patient treated in this fashion again obtains good vision.
In phacoemulsification, use is made of a device that in general has a source with irrigation fluid, an irrigation fluid line for supplying irrigation fluid to the ocular lens to be treated, a needle that can oscillate and is in a handpiece, and a suction line (aspiration line) for removing emulsified lens fragments into a collection container.
The irrigation fluid source is arranged higher up than the ocular lens to be treated, and so the irrigation fluid or rinsing fluid can flow to the eye with hydrostatic pressure. Depending on application, the irrigation fluid source can usually be displaced to different heights, and so a different hydrostatic pressure can be obtained. For this purpose, the irrigation fluid source is hung onto a rod that can be driven by a motor and thus attains various heights. Such displacement of the irrigation fluid source involves a few seconds for the desired height to be reached. Furthermore, it can be necessary to wait for pressure variations induced by the displacement of the irrigation fluid source to have died down before an operation can be continued. The height of the displacement of such a source has mechanical limits due to the rod. Hence, the maximum hydrostatic pressure of the irrigation fluid is prescribed by the achievable height of the irrigation fluid source.
In practice it was found that different operations on the eye can involve different fluid pressures. An operation on the front section of the eye can involve a different pressure than an operation on the back section of the eye. Moreover, different operations in each case can involve different instruments, such as needles with differing diameters for a phacoemulsification handpiece, wherein work is undertaken with different pressures. The fluid pressures that can be achieved in currently available systems for phacoemulsification often do not suffice for such applications.
Additionally, there is a trend in minimally invasive surgery for an incision to be carried out with ever smaller instruments or needles. The reason for this trend mainly lies in the fact that post-operative treatment of a patient has to be carried out less often as the size of the cut carried out in the operation decreases. In the case of a very small cut, there may be no need for aftercare, and so no further complications may occur. The use of hollow needles with very small diameters, e.g. greater than 23 gauge, however can mean a high tube friction coefficient for the flowing fluid. For comparison, reference is made to the fact that an external diameter of 25 gauge corresponds to an outer diameter of 0.5 mm. However, as the diameter of the needle decreases, the pressure with which the fluid is transported through the pipe line or needle generally increases in order to achieve the same fluid volume flow. In the known ophthalmosurgical systems, the available fluid pressure often does not suffice for this.
Additionally, a higher irrigation fluid pressure may be desired very quickly during an operation. Displacing the irrigation fluid source then may involve too much time and/or may not provide the desired pressure, and so complications during the operation may occur.